KR100974786B1 - Elastic nonwoven sheet - Google Patents

Abstract

The present invention relates to an extensible nonwoven sheet prepared by treating the necked nonwoven substrate with an elastomeric polymer solution to substantially uniformly impregnate the elastomeric polymer. This nonwoven sheet is useful for the production of diapers and other hygiene articles.

Extensible nonwoven sheets, elastomeric polymers, neck-bonded laminates, gripping forces.

Description

Elastic Nonwoven Sheet

The present invention relates to stretchable nonwoven sheets suitable for use in the manufacture of personal care articles. More specifically, the extensible nonwoven sheet is formed by substantially uniformly impregnating the necked nonwoven substrate with an elastomeric polymer.

Elastic nonwoven materials are well known in the art. Examples of elastic nonwoven materials include "stretch-bonded" and "neck-bonded" laminates. Stretch-bonded laminates are made by bonding a gatherable layer to an elastic layer in an elongated state and relaxing the elastic layer to crease the wrinkled layer. Neck-bonded laminates are made by combining the necked inelastic layer with an elastic film or fiber layer. The elastic layer generally comprises an elastic film or an elastic nonwoven web. These elastic nonwoven laminates require the production of at least two separate nonwoven or film layers.

U.S. Pat. No. 4,366,814 (Reidel) is a breathable elastic bandage comprising at least 50 wt% stretchable fabric that can be stretched at least 30% without tearing and at least 15 wt% elastic body impregnated in the fabric without filling the holes in the fabric. The material is described.

U.S. Patent No. 5,910,224 (Morman) applies an elastomeric precursor to a neckable material such as a nonwoven web, neck stretches the neckable material, and treats the elastomeric precursor by heating or the like while the neckable material is necked. A method of making an extensible composite is described by forming an elastomeric layer bonded to a necked material. Preferred elastomeric precursors include latex or thermoset elastomers. The elastomeric precursor is applied to the neckable material in an amount of 5 g / m 2 to about 50 g / m 2. The elastomeric layer preferably penetrates the web at about 2 to about 10 fiber thicknesses and the extent of permeation of the elastomeric precursor is controlled such that it does not penetrate to the opposite side of the web side to which the elastomeric layer is applied. Thus, the resulting stretchable composite has a film-like feel on the side that includes the elastomeric layer, while maintaining the soft hand inherent to the neckable material on the opposite side of the elastomeric layer.

European Patent Application Publication No. 0472942 is compressible and recoverable in the Z-direction, comprising a fibrous web saturated with a polymeric material such as elastomeric acrylic latex, polyurethane latex or nitrile rubber latex, such as a nonwoven web of meltblown fibers. Elastomeric saturated nonwoven materials having properties have been described.

Japanese Patent Application Laid-Open No. 47-24479 relates to a belt for a conveyor and a transmission device manufactured by impregnating a needle punched nonwoven fabric with rubber or synthetic resin.

There is still a need for elastic sheet materials that can be produced economically, have soft stretchability and good holding power, and have a fabric-like feel on both sides.

Brief summary of the invention

The present invention

Providing a necked nonwoven substrate having a thickness, first and second outer surfaces, a machine direction and a transverse direction, and having a percent elongation of at least 30% in the transverse direction;

Substantially uniformly impregnating the necked nonwoven substrate with a solution comprising an elastomeric polymer dissolved in a solvent;

The solvent is removed from the nonwoven substrate impregnated by wet coagulation, so that the elastomeric polymer is the entire thickness of the nonwoven substrate, without forming a substantially continuous elastomeric polymer layer on either of the first or second outer surfaces of the nonwoven substrate. Depositing substantially uniformly on

A method for producing an extensible nonwoven sheet.

The present invention also includes a nonwoven substrate that is necked in the necking direction and substantially uniformly impregnated with an elastomeric polymer, and is stretched three times to 140% in the necking direction and then at 100% stretching in a third unload cycle. A stretchable nonwoven sheet having a ratio of force at 100% elongation of a third load cycle to 0.3: 1 or more.

In the present invention, an extensible composite nonwoven sheet is provided by impregnating a necked nonwoven substrate with a solution comprising a solvent and an elastomeric polymer. The necked nonwoven substrate is impregnated under conditions where a substantially uniform impregnation of the nonwoven substrate is achieved without a polymer layer being formed on either surface thereof. After removal of the solvent, a breathable impregnated nonwoven sheet is obtained having an unexpected combination of high no-load cycle forces (meaning good retention and smooth elongation) and textile-like feel compared to the load cycle forces in the transverse direction. In addition, the sheets of the present invention are typically simpler and thinner to manufacture than conventional multilayer stretch laminates. For example, the sheet of the invention may typically have a thickness of about 0.25 mm to 0.75 mm, while the stretch stack is generally thicker than 1.3 mm.

The term "polymer" as used herein generally includes, but is not limited to, homopolymers, copolymers (eg, block, graft, random and alternating copolymers), terpolymers, and the like, and blends and modifications thereof. Does not. Also, unless expressly limited otherwise, the term "polymer" includes all possible geometrical forms of the material. These forms include, but are not limited to, isotactic, syndiotactic, and random symmetry.

The term "polyester" as used herein includes polymers wherein at least 85% of the repeating units are condensation products of dicarboxylic acids and dihydroxy alcohols bonded by the formation of ester units. This includes aromatic, aliphatic, saturated, and unsaturated di-acids and di-alcohols. As used herein, the term “polyester” also includes copolymers (eg, block, graft, random and alternating copolymers), blends, and variants thereof. Typical examples of polyesters are poly (ethylene terephthalate) (PET), which is a condensation product of ethylene glycol and terephthalic acid.

As used herein, the term "polyurethane" includes block copolymers prepared by condensing difunctional polyols with diisocyanates and difunctional chain extenders.

As used herein, the term "polyolefin" means any series of highly saturated open chain polymer hydrocarbons consisting solely of carbon and hydrogen. Typical polyolefins include, but are not limited to, polyethylene, polypropylene, polymethylpentene, and various combinations of ethylene, propylene, and methylpentene monomers.

The term "polyethylene" as used herein includes not only homopolymers of ethylene, but also copolymers in which at least 85% of the repeat units are ethylene units.

The term "polypropylene" as used herein includes not only homopolymers of propylene, but also copolymers in which at least 85% of the repeat units are propylene units.

The term "elastomeric polymer" as used herein, when formed into a sheet, fiber or film, can be stretched to an elongated length of at least about 160% of its relaxed unbiased length when relaxed under tension, and relaxes the stretch deflection force. When it refers, it points to the arbitrary polymer which recovers 55% or more of the extending | stretching. For example, a 1 cm sample of this material may be stretched to 1.6 cm or more and will recover to a length of 1.27 cm or less when stretched to 1.6 cm after applying force and then relaxed. There are various elastomeric materials that can be stretched far more than 60% of their relaxed length, for example up to 100% or more, many of which are substantially at their original relaxed length upon relaxation of the stretching force, eg For example, it will recover to within 105% of its original relaxed length.

As used herein, the term "nonwoven" or "nonwoven web" refers to a structure of individual fibers, filaments, or yarns that, in contrast to a knitted fabric or woven fabric, are arranged in a random manner to form a planar material without an identifiable pattern.

As used herein, the term "spunbond" filament refers to a filament formed by rapidly reducing the diameter of such extruded filaments by stretching while extruding molten thermoplastic polymer material from a plurality of fine, usually circular spinneret capillaries. do. Other fiber cross-sectional shapes such as ovals, multi-lobal, and the like may also be used. Spunbond filaments are generally continuous and have an average diameter of greater than about 5 micrometers. Spunbond nonwoven webs are formed by randomly depositing spunbond filaments on a collecting surface, such as a perforated screen or belt. Spunbond webs are generally joined in a manner known in the art, for example by hot-roll calendering or by passing the web through a saturated vapor chamber at elevated pressure. The web is also point bonded by heat at a plurality of thermal bond points located throughout the spunbond nonwoven surface.

As used herein, the term "machine direction (MD)" refers to the direction in which the nonwoven web is produced. The term "lateral direction (XD)" generally refers to a direction perpendicular to the machine direction.

As used herein, the term "necking" refers to, for example, applying a force to a nonwoven in parallel to the machine direction of the nonwoven, thereby stretching the nonwoven in the direction of applying the force and in a direction perpendicular to the stretching direction, for example in a transverse direction. Refers to a controlled manner and a method of reducing the width to a desired amount. The direction perpendicular to the stretching force is referred to herein as the "necking direction". Controlled stretching and necking can be carried out at room temperature or at temperatures above or below room temperature, and the overall dimensional increase in the direction of stretching is limited to below the stretch required for the nonwoven to tear or break.

As used herein, the terms "necked nonwoven" and "necked nonwoven substrate" refer to any nonwoven that has been shrunk in one or more directions by a process such as stretching. "Neckable nonwoven" is a nonwoven that can shrink in one or more dimensions in a necking process. The term "percent neckdown" measures the difference between an unnecked dimension and a necked dimension (measured in the necking direction), divides this difference by the unnecked dimension, and multiplies the resulting ratio by 100. Point to the rain obtained. The necked nonwoven fabric is generally stretchable in the necking direction by an amount corresponding to (but not in a linear relationship) the percent neckdown during the necking. Stretchability of necked nonwovens is an elongation obtained by stretching the necked nonwovens to the maximum possible extent in the necking direction, without stretching individual fibers inside the nonwovens, breaking the fiber-fiber bonds within the nonwovens, or tearing the nonwovens. Is measured.

As used herein, the term "wet coagulation" refers to a nonwoven substrate impregnated with a solution comprising an elastomeric polymer dissolved in a solvent that is miscible with the solvent used to form a nonsolvent or elastomeric polymer solution for the elastomeric polymer. It refers to the process of contacting with the coagulating solution. The coagulating solution is also chosen to not dissolve the nonwoven substrate. The coagulant solidifies the polymer material and removes the solvent into the coagulation liquid. The coagulating solution is then removed from the polymer impregnated nonwoven fabric by air drying or heating or the like.

Neckable nonwovens suitable for use in the present invention include spunbond webs, bonded carded webs, and hydroentangled webs. The neckable nonwoven fabric is necked transversely using methods known in the art to obtain a necked nonwoven substrate having a transverse elongation of about 30% to about 300%, with a percent neckdown of about 25% to about 75%. It is desirable to achieve this. Neckable nonwovens useful in the present invention can be prepared from a number of thermoplastic polymers including inelastic polyolefins such as polyethylene, polypropylene, ethylene copolymers, polyamides, polyesters, polystyrenes and poly-4-methylpentene-1. have. Preferably, the neckable nonwoven includes polypropylene, polyester, or polypropylene-polyethylene copolymer. In a preferred embodiment, the neckable nonwoven is a spunbond polypropylene nonwoven or a carded thermally bonded polypropylene or polyester nonwoven. The neckable nonwoven substrate as starting material preferably has a basis weight of about 10 g / m 2 to about 50 g / m 2. Particular preference is given to relatively low basis weight neckable nonwovens having a basis weight of, for example, from about 10 g / m 2 to about 20 g / m 2. It is preferable that a nonwoven substrate is water vapor permeable. The neckable nonwoven substrate is necked to provide a necked nonwoven substrate having a basis weight of generally greater than about 15 g / m 2.

Necked nonwovens are known in the art and are generally prepared by stretching the neckable nonwovens in the machine direction to provide a crosswise necked nonwoven. Examples of necking processes are disclosed, for example, in US Pat. Nos. 4,443,513 (Meitner), US Pat. Nos. 4,965,122, 4,981,747, and 5,114,781 (or Morman). Preferred necking processes are disclosed in US Reissue Patent No. 35,206 (Hassenboehler Jr. et al.). US Reissue Patent No. 35,206 is a reissue patent of US Patent No. 5,244,482. The nonwoven web necked according to Hässenöller's method is referred to herein as a "consolidated web."

Necked nonwovens can be manufactured using a relatively low cost process, have higher levels of lateral stretch, and other stretches because relatively low stretching (load) forces are required to stretch the nonwovens in the lateral direction. It is preferred over nonwoven fabrics. In addition, necked nonwovens are generally substantially non-extensible in the machine direction and have an elongation of less than about 5% when deflection forces are applied in the machine direction. Substantially stretching in one direction is highly desirable for the particular end use discussed below.

In a preferred embodiment, the necked nonwoven substrate is an integrated web made using the method described by Hassen Muller. This method passes a bonded thermoplastic nonwoven web having a relatively low workability through a heating zone, such as an oven, thereby increasing the temperature of the web to a temperature between the softening temperature and the melting temperature of the polymer web. Drawing to plastically deform the transversely oriented fibers and integrate (necking) the web in the transverse direction. Stretching is effected by feeding the web into the zone at a first linear velocity and withdrawing at a second linear velocity exceeding the first linear velocity. The ratio of second speed to first speed is preferably in the range of about 1.1: 1 to about 2: 1. The starting material, the bonded nonwoven web, is a necking non-elastic nonwoven and, during high temperature processing, at high temperature stretching at a strain rate of more than 2500% / min, and at a temperature above the softening point but at least 10 ° F. below the melting temperature of the polymer web. The elongation at break at the measured high temperature processing is selected to be less than about 4.0: 1 and greater than about 1.4: 1. The room temperature break elongation (strain) using an Instron tensile tester according to ASTM Test Method D 1117-77 is preferably 2 to 40%, more preferably 5 to 20%.

The fibers in the starting web can be joined by thermal bonding such as fiber-fiber fusion, fiber entanglement, or point bonding. Preferably, the fibers in the neckable nonwoven have a small average fiber diameter of less than about 50 micrometers, for example. The bonding of the spunbond precursor is preferably strong enough to locally stretch, twist and bend the filament segments without affecting the integrity of the web (eg, hot thermal bonding). In point bonding, the bonding point and the bonding pattern are generally selected such that the area of the bonding point is about 5 to about 25% of the web area. The shape of the bond point can be diamondoid or any of a variety of other shapes well known in the art.

The hot drawing process causes plastic deformation of the transverse fibers and integration of the web, causing the majority of the fibers to generally align in the drawing direction (machine direction). As the web is stretched in the longitudinal direction, it is laterally integrated and thermally fixed to the starting nonwoven.

An elastic nonwoven sheet of the present invention can be produced using a necked nonwoven substrate having a stretch in the cross direction of at least 30%, preferably at least 50%. The percent neckdown of the nonwoven web during the integration process is preferably about 50% to about 75%, more preferably about 60% to 70%, which is about 100% to 300% and 150% to 250%, respectively. Corresponds to

The basis weight of the necked nonwoven web may be at least three times greater than the basis weight of the starting neckable nonwoven web. Preferably, the basis weight of the necked web is about 15 g / m 2 to about 70 g / m 2, more preferably about 20 g / m 2 and about 70 g / m 2, most preferably about 25 g / m 2 to about 70 g / m 2. The basis weight of the necked nonwoven substrate is selected according to the desired end use. For example, when used as an elastic interliner, the basis weight of the necked nonwoven fabric is preferably 30 g / m 2 to 70 g / m 2, while in hygienic end applications such as diaper waistbands, the basis weight is about 15 g /. It is preferable that it is m <2> -40g / m <2>. The basis weight of the necked nonwoven substrate should also be chosen to achieve the desired elasticity of the final impregnated nonwoven fabric. The higher the basis weight of the nonwoven substrate will allow more elastomeric polymer to be impregnated into the nonwoven to increase the no-load force of the impregnated nonwoven sheet.

The use of a relatively low basis weight nonwoven fabric in the necking process described by Hassen Muller is preferred for the preparation of the material according to the invention. After being used with an elastomeric polymer to be impregnated with an elastomeric polymer, these factors combine to bring that the force (load force) required to stretch the material is relatively low and the shrinkage (no-load force) the material exhibits when relaxing the material is relatively high. Provide extensible nonwovens. This property is desirable for the end use in which this material will be used. The no-load force versus the load force is related to the hysteresis of the elastic nonwoven fabric. For the preferred product of the present invention having a transverse elongation of at least 150%, the impregnated nonwoven fabric is stretched up to 140% three times and relaxed between stretches, followed by a ratio of no-load force at 100% stretching to load force at 100% stretching. At least 1, preferably greater than 0.45: 1.

Elastomeric polymers useful in the present invention include polyurethanes, styrene-butadiene block copolymers and polyether-ester block copolymers. In a preferred embodiment, the elastomeric polymer is a polyurethane.

Elastomeric polyurethanes useful in the present invention react polymer polymers with diisocyanates to form capped glycols, dissolve the capped glycols (in a suitable solvent), and then the capped glycols are difunctional chain extenders with active hydrogen atoms. It can be prepared by reacting with. Such polyurethanes are said to be "segmented" because they consist of "hard" urethane and urea segments derived from diisocyanates and chain extenders and "soft" segments derived primarily from polymer glycols. to be. Suitable solvents for preparing solutions of such polymers are amide solvents such as dimethylacetamide ("DMAc"), dimethylformamide ("DMF") and N-methyl-pyrrolidone, but dimethyl sulfoxide and tetramethylurea Other solvents such as may also be used.

Polymer glycols used in the preparation of elastomeric polyurethanes include polyether glycols, polyester glycols, polycarbonate glycols and copolymers thereof. Examples of such glycols include poly (ethylene ether) glycol, poly (tetramethylene ether) glycol, poly (tetramethylene-co-2-methylene-tetramethylene ether) glycol, poly (ethylene-co-butylene adipate) glycol, Poly (2,2-dimethyl-1,3-propylene dodecanoate) glycol, poly (pentane-1,5-carbonate) glycol and poly (hexane-1,6-carbonate) glycol.

Useful diisocyanates include 1-isocyanato-4-[(4-isocyanatophenyl) methyl] benzene, 1-isocyanato-2-[(4-isocyanato-phenyl) methyl] Benzene, isophorone diisocyanate, 1,6-hexanediisocyanate and 2,4-tolylene diisocyanate.

The chain extender may be a diol or diamine. Useful diols include ethylene glycol, 1,3-trimethylene glycol, 1,4-butanediol and mixtures thereof. The use of diol chain extenders produces polyurethane. Useful diamines include ethylene diamine, 1,2-propanediamine, 2-methyl-1,5-pentanediamine, 1,3-diaminopentane, 1,4-cyclohexane-diamine, 1,3-cyclohexanediamine and these Mixtures thereof. In this case, the resulting polymer is polyurethaneurea (a subgroup of polyurethanes). When using polyether glycols and diamine chain extenders, the resulting polymer is polyetherurethane urea, and polyester urethaneureas are produced when polyester glycols are used in combination with polyamine chain extenders. Monofunctional amine chain stoppers such as diethyl amine, butylamine, cyclohexylamine and the like can be added to control the molecular weight of the polymer. In a preferred embodiment, the elastomeric polymer is a polyurethane elastomer extended with diamine.

Suitable solvents for preparing elastomeric polymer solutions include dimethylacetamide, dimethylformamide and N-methylpyrrolidone. The viscosity of the elastomeric polymer solution is directly related to the concentration of the polymer material in the solution, and as a result, the solution viscosity can affect both the degree of polymer penetration into the necked nonwoven and the amount of polymer deposited therein. have. If the solution viscosity is too low, an insufficient amount of elastomer can be deposited on the necked nonwoven substrate, causing a low no load force. If the solution viscosity is too high, solution penetration into the nonwoven substrate may be reduced such that the polymer is incompletely or unevenly impregnated into the nonwoven or a layer of polymer is formed on the surface of the necked nonwoven. The solution viscosity of the solution of elastomer to be impregnated into the necked nonwoven substrate is preferably about 1,000 to 300,000 centipoise (“cP”), more preferably 10,000 to 40,000 cP. The solution may comprise about 5 wt% to 20 wt% polymer.

The necked nonwoven substrate should be able to absorb the polymer solution and the polymer solution should be impregnated into the nonwoven substrate substantially completely and uniformly. Thus, the necked nonwoven substrate should not be coated or otherwise treated to prevent the polymer solution from absorbing into the necked nonwoven. Elastomeric polymer solutions and / or nonwovens may include surface active agents that facilitate the impregnation of the web with the polymer solution. Suitable surface active agents include nonionic wetting agents, such as polymeric surfactants.

Unless the benefit of the present invention is reduced, additives such as pigments, antioxidants, ultraviolet light stabilizers and lubricants may be added in small amounts to the elastomeric polymer solution.

The elastomeric polymer solution may be dispersed very short and fine fibers, such as wood pulp, cellulose fibers from cotton dust, or other synthetic fibers less than about 0.10 inch (2.5 mm) in length, or preferably less than 0.5 mm, or It may contain natural fibers. The fibers are preferably small enough to fully penetrate the nonwoven during the impregnation step. The short fibers may be added to the polymer solution in an amount sufficient to deposit about 3 to about 12 weight percent of the short fibers in the impregnated nonwoven sheet, calculated based on the total weight of the nonwoven / elastomeric polymer composite. Short fibers are preferably added to the elastomeric polymer solution at about 10 to about 30 weight percent, more preferably at about 10 to about 20 weight percent, based on the total weight of the short fibers, elastomeric polymer and solvent. The nonwoven sheet of the present invention prepared by impregnating the necked nonwoven fabric with an elastomeric polymer solution containing powdered cellulose may have a softer feel than that produced using an impregnation solution containing no short fibers. Examples of very thin fibrous particulate materials suitable for use in polymer solutions are Jay. Powdered cellulose under the trade name "Arbocel 30" sold by J. Rettenmaier USA (Schocraft, Michigan, USA).

Elastomeric polymer solution is coated onto the necked nonwoven substrate or any other impregnated nonwoven substrate unless the nonwoven is uniformly impregnated and the coating is not concentrated on one or the other surface of the necked nonwoven substrate. Appropriate methods can be used. Coating methods may also be used to treat the necked nonwoven substrate with an elastomeric polymer solution, but the solution and nonwoven characteristics and coating process conditions completely wet the nonwoven substrate with the polymer solution necked or the polymer solution completely into the nonwoven substrate. It should be chosen so that the polymer layer is absorbed or induced so that no polymer layer is formed on either surface of the nonwoven substrate. In general, the amount of polymer solution applied during coating can be controlled using a coating tool that maintains a predetermined distance over the necked nonwoven. The solution may also be mechanically pressed into the necked nonwoven substrate. Rollers, platens, scrapers, knives and the like may be used as coating tools in the process of the present invention. Spraying the solution onto the necked nonwoven substrate may also be effective as long as the elastomeric solution is substantially completely and uniformly impregnated into the nonwoven substrate. The force of the spray can be adjusted to help achieve good permeability. In the art, a "dip and squeeze" method, in which a fibrous web is immersed or otherwise immersed in a tank containing an elastomeric polymer solution and then squeezed between nip rolls or the like to remove excess polymer solution. Known methods can be used to impregnate the necked nonwoven substrate with an elastomeric polymer solution. This method is desirable to reduce the difference between the two surfaces of the stretchable composite nonwoven sheet.

The necked nonwoven substrate is impregnated with sufficient polymer solution to provide the desired no-load / load force in the final impregnated nonwoven sheet. The necked nonwoven substrate is a polymer solution sufficient to allow about 15 to about 55 weight percent, more preferably about 30 to about 50 weight percent, of elastomeric polymer to be deposited therein based on the total weight of the elastomeric polymer and the nonwoven substrate. It is preferable to impregnate with. If the amount of elastic body is too small, the ratio of no-load force to load force may be undesirably low, and if the amount of elastic body is too large, the texture of the sheet surface may be undesirably sticky. The solution concentration and / or the amount of solution impregnated into the necked nonwoven can be adjusted to achieve the desired polymer content in the impregnated sheet. For example, using a low polymer concentration in a solution and maintaining a similar elastomer content on the impregnated sheet by widening the gap between the nip rolls upon application of the solution, the balance of tactile and no-load / load force ratios An improved product was obtained.                 

After impregnating the nonwoven substrate with a solution comprising a solvent and an elastomeric polymer, the solvent is removed. The solvent is removed by wet coagulation followed by removal of the coagulation liquid. Wet coagulation provides a product that is surprisingly softer and has a more cloth-like feel compared to thermal drying. Wet coagulation processes are well known in the art and are commonly used in the manufacture of artificial leather. Water is preferable as a coagulating liquid because it is easy to handle and inexpensive. Other suitable coagulants include methanol, ethanol, isopropanol, acetone or methyl ethyl ketone. Solvents for elastomeric polymers, such as dimethylformamide, dimethylacetamide or N-methyl-pyrrolidone, or other additives, such as surfactants, may be added to the coagulant to alter the rate of coagulation. It is also possible to change the coagulation rate by adjusting the temperature of the coagulation bath. The slower the solidification rate, the better the feel is obtained after the solvent is removed.

In the impregnated nonwoven sheet of the present invention, the elastomeric polymer phase uniformly distributed throughout the necked nonwoven substrate is breathable. In addition, the impregnated nonwoven sheet is preferably water vapor permeable.

The feel of the impregnated nonwoven sheet can be improved to provide a softer feel by raising the fibers on the surface of the impregnated sheet by sanding or napping. Napping involves passing the nonwoven over a rotating roll with a small metal point for effectively brushing the nonwoven to raise the fiber to the surface. In sanding, the metal brush is replaced with a rolling roll coated with sandpaper. Preferably, both sides of the impregnated nonwoven fabric are sanded or napped. For example, the nonwoven can be sanded with 80 to 200 grit sandpaper.

The impregnated extensible nonwoven sheet of the present invention preferably has a basis weight of about 40 g / m 2 to about 100 g / m 2. It is also useful for waistbands or side panels of diapers or other disposable personal care garments. Diapers are assembled on commercially long, high speed lines, where it is generally desirable to add various diaper parts in the machine direction to avoid process delays. This is especially the case for elastomeric materials which usually stretch before insertion. Diapers generally include at least about 20 individual parts, all of which must be accurately placed in the correct position on the diaper during the high speed manufacturing process. This can be achieved much more easily when feeding parts (tape, sheets, fibers, etc.) in the same direction as the diaper moves. In order to add the components laterally (eg waistband), the material itself is preferably stretched laterally so that it can be fed into the diaper manufacturing process as a tape in the machine direction. For example, the tape may be a piece that is 7 inches wide and only 1 inch long that is cut from the sheet and attached to a diaper or other disposable undergarment. In addition, in such a process, it is preferable that the diaper parts supplied into the process be substantially non-extensible in the machine direction in order to easily supply the process into the process. The stretchable nonwoven sheet of the present invention is particularly suitable for use in such processes because it is substantially non-extensible in the machine direction and has a high recoverable stretch in the transverse direction.

Test Methods

Basis weight

A sample of about 1.0 inch by 8.0 inch (2.54 cm by 20.32 cm) rectangular nonwoven sheet was carefully relaxed to ensure that the sample was not wrinkled or wrinkled. The length and width of the sample were measured in millimeter approximations and the samples were weighed in 1/10 approximate milligrams. The weight was divided by the calculated area and the results were expressed in g / m 2 of 0.1 gram approximation.

Load force and No load  Force analysis

The analysis was performed on an Instron Model 5565 equipped with a Merlin data acquisition software system. Merlin system and device hardware are all available from Instron Corporation (Braintree, Massachusetts, USA). A sample of nonwoven sheet having a width of 1 ± 0.05 inches (2.54 cm ± 0.13 cm) and approximately 8 inches (20.32 cm) in length was placed in the jaw of the Instron machine with the sample length set to 3.00 inches (7.62 cm). Bite. The sample was prepared so that the length of the sample coincided with the transverse direction of the nonwoven fabric. The sample was stretched to 140% stretching at a rate of 6 inches / minute (15.24 cm / minute) and then relaxed to its original length. Repeat this two more times and record the force (load force) the material exhibits in the draw cycle at the third cycle at 50%, 100% and 135% stretch based on the original sample length, and similarly the material exhibits at the third relaxation cycle. Force (no load force) was also recorded at the same draw point. The results are expressed in grams with the third cycle load force and no load force at the appropriate elongation.

Elongation  (percent elongation) analysis

With a pen at approximately the same distance from the end of the nonwoven, two points, 4.0 inches (10.2 cm) apart on a relaxed nonwoven strip about 1.0 inches (2.54 cm) wide and about 8 inches (20.32 cm) long, without wrinkles or wrinkles Indicated. The end of the nonwoven was then firmly gripped with the thumb and index finger of both hands, but the sample was drawn completely, but not stretched enough to tear or cause any similar physical damage. The maximum stretching point can be clearly seen from the marked increase in the stretching resistance of the nonwoven fabric of the self performing the test. Subsequently, the distance between the two points marked on the nonwoven fabric was measured, and the elongation was calculated by the following formula (wherein, the initial length was 10.2 cm).

Elongation = {(stretched length-initial length) / initial length} × 100%

When the elongation was measured in the necking direction, the nonwoven fabric sample was cut so that the length of the sample coincided with the transverse direction (necking direction).

A 30-inch (76.2 cm) 15 g / m2 wettable spunbond polypropylene nonwoven fabric made from Avgol Nonwovens (Israel) was fed to the nip roll at 89 ft / min (27 m / min). After passing through a 72 inch (1.83 m) length 290 ° F. (143 ° C.) forced air oven to a second nip roll operated at 115 ft / min (35 m / min), it was wound on a take-up roll. In this process, a 30 inch (76.2 cm) wide nonwoven fabric was uniformly and smoothly integrated ("necking") with a width of 10 inches (25.4 cm) in the transverse direction. This nonwoven fabric could be stretched back to its original 30 inch (76.2 cm) transverse width with minimal force. The necked nonwovens had an essentially zero mechanical direction stretch and a basis weight of 32.0 g / m 2.

One side of the necked nonwoven fabric was 15 mil (0.38 mm) doctor knife, and poly (tetramethylene ether) glycol, molecular weight 1800, 1-isocyanato-4-[(4-isocyanatophenyl) methyl] benzene (Weight ratio of diisocyanate to glycol is 1.69), chain extenders (ethylene diamine and 2-methyl-1,5-pentanediamine in molar ratio 9: 1) and 20% by weight of urea polyurethaneurea derived from diethylamine Coated with acetamide (DMAC) solution. In addition, a polymer of bis (4-isocyanatocyclohexyl) methane and (3-t-butyl-3-aza-1,5-pentanediol) (methacrol (registered trademark) 2462B, IIA DuPont Di) 0.5% by weight of registered trademark of EI du Pont de Nemours and Company, 0.3% by weight of titanium dioxide, 0.6% by weight of silicone oil, 2,4,6-tris (2,6-dimethyl-4- t-butyl-3-hydroxybenzyl) isocyanurate (Cyanox® 1790, registered trademark of Cytec Industries) 1.4% by weight and 4% by weight of a mixture of hottite and hydromagnesite Was used as an additive (all of which are percentages based on polyurethaneurea weight). The nonwoven was fully wetted with the polyurethaneurea-DMAC solution.

The coated nonwoven was suspended in air substantially vertically for about 1 minute to allow the polymer solution to fully penetrate into the nonwoven and then immersed in 40% by volume DMAC bath in 70 ° F. (21 ° C.) water. After 1 minute, the impregnated nonwoven was continuously transferred to 30%, 20%, and 10% by volume of the solution for 1 minute each, and finally soaked in 100% water for 2 minutes. The impregnated nonwoven fabric was dried in air at room temperature.                 

The resulting impregnated nonwoven sheet had a tactile (dry and textile-like) feel on both sides. Micrographs of the cross section of the impregnated nonwoven sheet showed a uniform composite structure throughout the thickness of the material, with substantially no continuous polyurethane regions on either surface.

The nonwoven sheet was then sanded with 220 grit sandpaper. The resulting material had a remarkably soft hand, and when viewed with the naked eye, many individual short fibers were extending from the surface compared to the completely smooth surface without the fibers that were stretched before sanding. It is not expected that this treatment will be successful in providing a softer feel without significantly compromising the visual aesthetic or elastic properties of the sheet.

The resulting impregnated nonwoven sheet had a basis weight of 71.4 g / m 2, indicating a polyurethaneurea content of 39.4 g / m 2 or about 55% by weight of elastomeric polymer.

The transverse elongation of the resulting material, measured by hand, showed an elongation of about 160% to 180%. Load and no load force analysis results are shown below.

Third load cycle force

Elongation (%) Load force (g) 50 67.3 100 211.2 135 409.7

The third No load  Cycle power

Elongation (%) Load force (g) 50 22.7 100 114.7 135 340.7

A comparison of the data in the table shows that the ratio of no-load force to load force at 0.5% stretching is 0.54.

Claims (10)

Providing a necked nonwoven substrate having a thickness, a first outer surface and a second outer surface, a machine direction and a transverse direction, and having a percent elongation of at least 30% in the transverse direction; Uniformly impregnating the necked nonwoven substrate with a solution comprising an elastomeric polymer dissolved in a solvent; The solvent is removed from the nonwoven substrate impregnated by wet coagulation, so that the elastomeric polymer is the entire thickness of the nonwoven substrate, without forming a continuous elastomeric polymer layer on either the first outer surface or the second outer surface of the nonwoven substrate. Comprising depositing uniformly to, Method for producing an extensible nonwoven sheet. The method of claim 1 wherein the elongation of the necked nonwoven substrate is less than 5% in the machine direction and the transverse elongation is between 100% and 300%. The method of claim 1, further comprising sanding or napping one or more of the outer surfaces of the nonwoven sheet after removing the solvent to produce fibers on the surface of the sheet. The method of claim 1, wherein the elastomeric polymer is deposited on the substrate at 15 to 55% by weight based on the total weight of the substrate and the elastomeric polymer. A shrinking force exhibited by the material when it relaxes the material at 100% elongation of the third unload cycle after stretching three times to 140% in the necking direction, including a necked nonwoven substrate uniformly impregnated with an elastomeric polymer. An extensible nonwoven sheet having a ratio of no load force and a force (load force) required to stretch the material at 100% stretching of the third load cycle at least 0.3: 1. The stretchable nonwoven sheet of claim 5 wherein the ratio of no-load force to load force is greater than 0.45: 1. 6. The stretchable nonwoven sheet of claim 5 comprising 30 to 50 percent by weight elastomeric polymer, based on the total weight of the elastomeric polymer and the nonwoven substrate. The stretchable nonwoven sheet of claim 5 having a basis weight of 40 g / m 2 to 100 g / m 2. A personal care garment comprising the stretchable nonwoven sheet of claim 5. 10. The personal care garment of claim 9 wherein the garment comprises a diaper.